Conventionally, display devices which each project an image in midair have been studied. In particular, from among these display devices, a display device is proposed which transmits an image to be projected in midair by using a light guide plate in order to make the image projected in midair visible simultaneously with another object (for example, see Patent Document 1).
For example, the display device disclosed in Patent Document 1 includes an emission mechanism which includes: a display element that emits image display light and an optical system that forms a virtual image of an observation target; and a light guide. The light guide is a substrate. The light guide includes a first surface, a second surface opposite to the first surface, a third surface which is neither the first surface nor the second surface, and an outgoing surface arranged in front of the eyes of an observer. The outgoing surface includes a plurality of beam splitters each having a planer shape. This display device causes image display light from the emission mechanism to enter the inside of the substrate of the light guide via the third surface. Then, the display device guides the image display light in a setting direction by means of the first surface and the second surface, and guides the image display light from the outgoing surface to the eyes of the observer.